1. Field of the Invention
This invention relates to new photographic compounds which release photographically useful groups during photographic processing and to photographic materials and processes using such compounds.
2. Description of the State of the Art
Various ways are recognized in the photographic art for release of a photographically useful group (PUG) from a compound, such as a coupler, in photographic materials and processes. For example, U.S. Pat. No. 4,248,962, describes compounds that release a photographically useful group by means of an intramolecular nucleophilic displacement reaction in photographic materials. Other examples are described in U.S. Pat. No. 4,409,323, wherein couplers are described which release a photographically useful group by means of an electron transfer down a conjugated chain. These compounds capable of releasing a photographically useful group in a photographic material upon processing provide a degree of control over the timing and rate of release as well as the rate of diffusion and distance of diffusion of the photographically useful group in the photographic material.
A need has continued to exist for a higher degree of control over these parameters as well as a higher degree of freedom in the capability to design compounds having releasable photographically useful groups. Moreover, such needs have existed with the added parameter that such compounds must not require significantly modifying the photographically useful groups or the carrier compounds, such as the couplers, from which the photographically useful group are released, in a way which would be inconsistent with the ultimate use for which each is intended.